The measurement and prediction of the corrosion potential of copper in chloride solutions as a function of oxygen concentration and mass-transfer coefficient

Abstract

Steady-state corrosion potentials of copper in O 2-containing NaCl solution have been measured using three types of electrode: a rotating-disc electrode, an electrode covered by a porous nylon membrane and an electrode covered by a layer of compacted Na-bentonite clay. Mass-transfer coefficients for these electrodes vary from 10 −2 cm s −1 in bulk solution to 10 −7 cm s −1 for the clay-covered electrode. Solutions were equilibrated with atmospheres of air, 2% O 2/N 2, 0.2% O 2N 2, or were nominally deaerated. In aerated bulk solution, the anodic reaction is mass-transfer limited and the cathodic reaction is kinetically controlled. With decreasing [O 2], the cathodic reaction becomes partially mass-transfer limited. Both reactions are essentially mass-transfer controlled for the membrane- and clay-covered electrodes. A mixed-potential model is developed for predicting E Corr over a wide range of mass-transfer conditions and [O 2], under circumstances where either reaction may be under joint kinetic/mass-transfer control.